This project aims to understand how nuclear and mitochondrial genomes contribute to adaptive evolution, and to discern the impact of sexual reproduction on this process. The cells of most non-microbial life forms contain numerous mitochondria, organelles responsible for generating biological energy. Mitochondria contain their own genomes, which are far smaller than "regular" nuclear genomes and encode a unique set of genes related to energy metabolism. Proper mitochondrial functioning relies upon many gene products encoded by the nuclear genome. These two genomes must therefore evolve in concert; i.e., mitonuclear coevolution. This research will provide the first comprehensive assessment of nuclear and mitochondrial genomic change accompanying controlled, adaptive evolution under different reproductive systems. It will also result in discovery of novel mutations that suppress the effects of mitonuclear damage. The project will provide important data and resources to the scientific community, expand the PIs' educational and outreach activities, and provide research training and professional development for a postdoctoral fellow, a research technician, and graduate and undergraduate students. Analysis of mitochondrial genomes has long been used for forensic and phylogenetic applications, and defects in mitochondrial genomes are implicated in approximately 1,000 human genetic diseases, cancer and aging. The central importance of mitochondrial genetics and mitonuclear interaction to diverse areas of biological research suggest that this research will have far-reaching impacts.

This research will provide the first direct, non-retrospective tests of major hypotheses to explain mitonuclear genome coevolution. The project will apply experimental genomics with Caenorhabditis elegans nematodes to study evolutionary process within the context of the mitochondrial electron transport chain (ETC), the proper functioning of which relies on the maintenance of favorable mitonuclear epistatic interactions. The project will: 1) Determine the impact of sexual system on the tempo and patterns of mitonuclear adaptation. C. elegans strains containing deleterious mitochondrial- and nuclear-encoded ETC mutations will undergo adaptation in replicate populations experiencing obligate selfing, facultative outcrossing, or obligate outcrossing, and 2) Determine the evolutionary dynamics, functional characteristics and sex-specific effects of individual mitonuclear mutations. Genomic, bioinformatic and phenotypic analyses will determine the molecular bases and functional underpinnings of mitochondrial and nuclear mutations available to mask the effects of deleterious ETC mutations, and reveal the relationship between rates of outcrossing and mitonuclear adaptation.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

National Science Foundation (NSF)
Division of Molecular and Cellular Biosciences (MCB)
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Stephen DiFazio
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Texas A&M Agrilife Research
College Station
United States
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